The invention concerns a method for inserting contact pins with an compliant attachment zone, which are generally mounted in the housing of a connector (so-called "press-fit" connector), in corresponding holes of a printed circuit board or of another part.
For inserting the connectors, equipped with compliant contact pins into a printed circuit board, use is generally made of a press, which must insert the contact pins. of the connector into the corresponding holes of the board, and must deform the compliant attachment zone of each pin such that the complete connector is secured to the board.
As is generally known, a contact pin with an compliant attachment zone consists of an elongated rod, usually with a square cross-section, where a part of the rod is cut in half longitudinally in order to form two legs next to each other, each of which is bent outwards in order to obtain an compliant attachment zone.
When inserting a pin into a hole in the board, the first non-compliant section of the pin is first inserted into the board, thus obtaining initial guidance for the pin, whereby virtually no resistance force will be induced.
When the compliant zone reaches the upper edge of the hole, the insertion force increases, and the legs which are bent outwards will move towards each other in an elastic manner in order to generate a retention force by the pin against the wall of the hole.
The insertion force that is required to perform this operation can be substantial, especially when the connector is equipped with a large number of contact pins which must be secured in their corresponding holes.
The major problem that is immediately apparent is stopping the downward movement of the press in time, in order to prevent any damage or deformation to the circuit board due to contact between the connector housing and the board.
Existing presses are usually provided with computer-controlled unit, and are equipped with a force measuring device that is incorporated in the head of the press and can measure and control the progress of the force/insertion curve.
For example, the press can be stopped when the developed force reaches a certain maximum value.
In practice, this can however lead to serious problems, since for presses of this capacity the inertia of the downward movement should not be underestimated, and can result in the housing of the connector being pressed against the board with excessive force, possibly resulting in damage to the board.
It is known for the insertion force of the press to increase by 1000 Newton per 0.01 mm at the end of the insertion cycle, when the housing of the connector comes into contact with the board.
It is also not possible to pre-set the correct maximum insertion depth since the thickness tolerance of the printed circuit board (PCB), which is normally 3.2 mm, is difficult to control. Thickness deviations of 10 to 12% are usual for the boards. In practice, these thickness deviations vary by several tenths of a millimeter since in this case, they relate to a laminated composite board.
In order to prevent over-pressing, it is consequently desirable to stop the press in good time in order to prevent the pressing movement from continuing after the housing of the connector has come into contact with the board.
In many applications, it is also desirable to leave an air gap between the connector housing and the surface of the circuit board.